Understanding 802.1X Port-Based Authentication

802.1X defines 802.1X port-based authentication as a client-server based access control and authentication protocol that restricts unauthorized clients from connecting to a LAN through publicly accessible ports. An authentication server validates each supplicant (client) connected to an authenticator (network access switch) port before making available any services offered by the switch or the LAN.

Note 802.1X support requires an authentication server that is configured for Remote Authentication Dial-In User Service (RADIUS). 802.1X authentication does not work unless the network access switch can route packets to the configured authentication RADIUS server. To verify that the switch can route packets, you must ping the server from the switch.

Until a client is authenticated, only Extensible Authentication Protocol over LAN (EAPOL) traffic is allowed through the port to which the client is connected. After authentication succeeds, normal traffic can pass through the port.

To configure 802.1X port-based authentication, you need to understand the concepts in these sections:

Device Roles

With 802.1X port-based authentication, network devices have specific roles. Figure 29-1 shows the role of each device, which is described below.

Figure 29-1 802.1X Device Roles

•Client—The workstation that requests access to the LAN, and responds to requests from the switch. The workstation must be running 802.1X-compliant client software.

Note For more information on 802.1X-compliant client application software such as Microsoft Windows 2000 Professional or Windows XP, refer to the Microsoft Knowledge Base article at this URL: http://support.microsoft.com

•Authenticator—Controls physical access to the network based on the authentication status of the client. The switch acts as an intermediary between the client and the authentication server, requesting identity information from the client, verifying that information with the authentication server, and relaying a response to the client. The switch encapsulates and decapsulates the Extensible Authentication Protocol (EAP) frames and interacts with the RADIUS authentication server.

When the switch receives EAPOL frames and relays them to the authentication server, the Ethernet header is stripped and the remaining EAP frame is reencapsulated in the RADIUS format. The EAP frames are not modified or examined during encapsulation, and the authentication server must support EAP within the native frame format. When the switch receives frames from the authentication server, the frame header is removed from the server, leaving the EAP frame, which is then encapsulated for Ethernet and sent to the client.

Cisco devices that are capable of functioning as an 802.1X network access point include Catalyst 4500 series switches, the Catalyst 3550 multilayer switch, the Catalyst 2950 switch, and a Cisco Airnet series wireless access point. These devices must be running software that supports the RADIUS client and 802.1X.

•Authentication server—Performs the actual authentication of the client. The authentication server validates the identity of the client and notifies the switch that the client is authorized to access the LAN and switch services. (The only supported authentication server is the RADIUS authentication server with EAP extensions; it is available in Cisco Secure Access Control Server version 3.2 and later.)

802.1x and Network Access Control

Network Access Control is a feature that allows port access policies to be influenced by the anti-virus posture of the authenticating device.

Anti-virus posture includes such elements as the operating system running on the device, the operating system version, whether anti-virus software is installed, what version of anti-virus signatures is available, etc. If the authenticating device has a NAC-aware 802.1X supplicant and the authentication server is configured to support NAC via 802.1X, anti-virus posture information will be automatically included as part of the 802.1X authentication exchange.

Authentication Initiation and Message Exchange

The switch or the client can initiate authentication. If you enable authentication on a port by using the dot1x port-control auto interface configuration command, the switch must initiate authentication when it determines that the port link state has changed. It then sends an EAP-request/identity frame to the client to request its identity (typically, the switch sends an initial identity/request frame followed by one or more requests for authentication information). Upon receipt of the frame, the client responds with an EAP-response/identity frame.

However, if during bootup, the client does not receive an EAP-request/identity frame from the switch, the client can initiate authentication by sending an EAPOL-start frame, which prompts the switch to request the client's identity.

If 802.1X is not enabled or supported on the network access device, any EAPOL frames from the client are dropped. If the client does not receive an EAP-request/identity frame after three attempts to start authentication, the client transmits frames as if the port is in the authorized state. A port in the authorized state means that the client has been successfully authenticated.When the client supplies its identity, the switch begins its role as the intermediary, passing EAP frames between the client and the authentication server until authentication succeeds or fails. If the authentication succeeds, the switch port becomes authorized.

The specific exchange of EAP frames depends on the authentication method being used. Figure 29-2 shows a message exchange that is initiated by the client using the One-Time Password (OTP) authentication method with an authentication server.

Figure 29-2 Message Exchange

Ports in Authorized and Unauthorized States

The switch port state determines whether or not the client is granted access to the network. The port starts in the unauthorized state. While in this state, the port disallows all ingress and egress traffic except for 802.1X protocol packets. When a client is successfully authenticated, the port transitions to the authorized state, allowing all traffic for the client to flow normally.

If a client that does not support 802.1X is connected to an unauthorized 802.1X port, the switch requests the client's identity. In this situation, the client does not respond to the request, the port remains in the unauthorized state, and the client is not granted access to the network. If the guest VLAN is configured for a port that connects to a client that does not support 802.1X, the port is placed in the configured guest VLAN and in the authorized state. For more information, see the "Using 802.1X Authentication for Guest VLANs" section.

In contrast, when an 802.1X-enabled client connects to a port that is not running the 802.1X protocol, the client initiates the authentication process by sending the EAPOL-start frame. When no response is received, the client sends the request a fixed number of times. Because no response is received, the client begins sending frames as if the port is in the authorized state.

You can control the port authorization state with the dot1x port-control interface configuration command and these keywords:

•force-authorized—Disables 802.1X authentication and causes the port to transition to the authorized state without any authentication exchange required. The port transmits and receives normal traffic without 802.1X-based authentication of the client. This setting is the default.

•force-unauthorized—Causes the port to remain in the unauthorized state, ignoring all attempts by the client to authenticate. The switch cannot provide authentication services to the client through the interface.

•auto—Enables 802.1X authentication and causes the port to begin in the unauthorized state, allowing only EAPOL frames to be sent and received through the port. The authentication process begins when the link state of the port transitions from down to up or when an EAPOL-start frame is received. The switch requests the identity of the client and begins relaying authentication messages between the client and the authentication server. The switch can uniquely identify each client attempting to access the network by the client's MAC address.

If the client is successfully authenticated (receives an Accept frame from the authentication server), the port state changes to authorized, and all frames from the authenticated client are allowed through the port. If authentication fails, the port remains in the unauthorized state, but authentication can be retried. If the authentication server cannot be reached, the switch can retransmit the request. If no response is received from the server after the specified number of attempts, authentication fails and network access is not granted.

If the link state of a port transitions from up to down, or if an EAPOL-logoff frame is received by the port, the port returns to the unauthorized state.

Using 802.1X with VLAN Assignment

You can use the VLAN assignment to limit network access for certain users. With the VLAN assignment, 802.1X-authenticated ports are assigned to a VLAN based on the username of the client connected to that port. The RADIUS server database maintains the username-to-VLAN mappings. After successful 802.1X authentication of the port, the RADIUS server sends the VLAN assignment to the switch. The VLAN can be a "standard" VLAN or a private VLAN.

On platforms that support Private VLANs, you can isolate hosts by assigning ports into PVLANs.

When configured on the switch and the RADIUS server, 802.1X with VLAN assignment has these characteristics:

•If no VLAN is supplied by the RADIUS server, the port is configured in its access VLAN when authentication succeeds.

•If the authentication server provides invalid VLAN information, the port remains unauthorized. This situation prevents ports from appearing unexpectedly in an inappropriate VLAN due to a configuration error.

Configuration errors might occur if you specify a VLAN for a routed port, a malformed VLAN ID, or a nonexistent or internal (routed port) VLAN ID. Similarly, an error might occur if you make an assignment to a voice VLAN ID.

•If the authentication server provides valid VLAN information, the port is authorized and placed in the specified VLAN when authentication succeeds.

•If the multiple-hosts mode is enabled, all hosts are in the same VLAN as the first authenticated user.

•If 802.1X is disabled on the port, the port is returned to the configured access VLAN.

•A port must be configured as an access port (which can be assigned only into "regular" VLANs), or as a private-VLAN host port (which can be assigned only into PVLANs). Configuring a port as a private-VLAN host port implies that all hosts on the port will be assigned into PVLANs, whether their posture is compliant or non-compliant. If the type of the VLAN named in the Access-Accept does not match the type of VLAN expected to be assigned to the port (regular VLAN to access port, secondary private VLAN to private VLAN host port), the VLAN assignment fails.

•If a guest VLAN is configured to handle non-responsive hosts, the type of VLAN configured as the guest VLAN must match the port type (that is, guest VLANs configured on access ports must be standard VLANs, and guest VLANs configured on private-VLAN host ports must be PVLANs. If the guest VLAN's type does not match the port type, non-responsive hosts are treated as if no guest VLAN is configured (that is, they are denied network access).

•To assign a port into a PVLAN, the named VLAN must be a secondary PVLAN. The switch determines the implied primary VLAN from the locally configured secondary-primary association.

•You cannot configure voice VLANs on a private VLAN port.

Note If the port mode is changed from private VLAN host mode to access mode when the port is authorized with a RADIUS-assigned private VLAN, the port is moved to the configured access VLAN. Similarly, when the port mode is changed from access mode to private VLAN host mode, the port is moved into the configured private VLANs.

Note If you configure a different VLAN when the port is authorized with a RADIUS-assigned private VLAN, the port remains in the RADIUS-assigned private VLAN, but the configured private VLAN is changed.

To configure VLAN assignment you need to perform these tasks:

•Enable AAA authorization with the network keyword to allow interface configuration from the RADIUS server. For an illustration of how to apply the aaa authorization network group radius command, refer to the section "Enabling 802.1X Authentication" on page 16.

•Enable 802.1X. (The VLAN assignment feature is automatically enabled when you configure 802.1X on an access port.)

•Assign vendor-specific tunnel attributes in the RADIUS server. To ensure proper VLAN assignment, the RADIUS server must return these attributes to the switch:

–Tunnel-Type = VLAN

–Tunnel-Medium-Type = 802

–Tunnel-Private-Group-ID = VLAN NAME

Using 802.1X Authentication for Guest VLANs

You can use guest VLANs to enable non-802.1X-capable hosts to access networks that use 802.1X authentication. For example, you can use guest VLANs while you are upgrading your system to support 802.1X authentication.

Guest VLANs are supported on a per-port basis, and you can use any VLAN as a guest VLAN as long as its type matches the type of the port. If a port is already forwarding on the guest VLAN and you enable 802.1X support on the network interface of the host, the port is immediately moved out of the guest VLAN and the authenticator waits for authentication to occur.

Enabling 802.1x authentication on a port starts the 802.1X protocol. If the host fails to respond to packets from the authenticator within a certain amount of time, the authenticator brings the port up in the configured guest VLAN.

If the port is configured as a private VLAN host port, the guest VLAN must be a secondary private VLAN. If the port is configured as an access port, the guest VLAN must be a regular VLAN. If the guest VLAN configured on a port is not appropriate for the type of the port, the switch behaves as if no guest VLAN is configured (that is, non-responsive hosts are denied network access).

Usage Guidelines for Using 802.1X Authentication with Guest VLANs on Windows-XP Hosts

The usage guidelines for using 802.1X authentication with guest VLANs on Windows-XP hosts are as follows:

•If the host fails to respond to the authenticator, the port attempts to connect three times (with a 30 second timeout between each attempt). After this time, the login/password window does not appear on the host, so you must unplug and reconnect the network interface cable.

•Hosts responding with an incorrect login/password fail authentication. Hosts failing authentication are not put in the guest VLAN. The first time that a host fails authentication, the quiet-period timer starts, and no activity occurs for the duration of the quiet-period timer. When the quiet-period timer expires, the host is presented with the login/password window. If the host fails authentication for the second time, the quiet-period timer starts again, and no activity will occur for the duration of the quiet-period timer. The host is presented with the login/password window a third time. If the host fails authentication the third time, the port is placed in the unauthorized state, and you must disconnect and reconnect the network interface cable.

Using 802.1X with Authentication Failed VLAN Assignment

You can use authentication failed VLAN assignment on a per-port basis to provide access for authentication failed users. Authentication failed users are end hosts which are 802.1X capable but do not have valid credentials in an authentication server or end hosts that do not give any username and password combination in the authentication pop-up window on the user side.

If a user fails the authentication process, that port is placed in the authentication-failed VLAN. The port remains in the authentication-failed VLAN until the reauthentication timer expires. When the reauthentication timer expires the switch starts sending the port re-authentication requests. If the port fails reauthentication it remains in the authentication-failed VLAN. If the port is successfully reauthenticated, the port is moved either to the VLAN sent by RADIUS server or to the newly authenticated ports configured VLAN; the location depends on whether RADIUS is configured to send VLAN information.

You can set the maximum number of authentication attempts that the authenticator sends before moving a port into the authentication-failed VLAN. The authenticator keeps a count of the failed authentication attempts for each port. A failed authentication attempt is either an empty response or an EAP failure. The authenticator tracks any mix of failed authentication attempts towards the authentication attempt count. After the maximum number of attempts is reached the port is placed in the authentication-failed VLAN until the reauthentication timer expires again.

Note RADIUS may send a response without an EAP packet in it when it does not support EAP, and sometimes third party RADIUS servers also send empty responses. When this happens, the authentication attempt counter is incremented.

Usage Guidelines for Using Authentication Failed VLAN Assignment

•You should enable reauthentication. The ports in authentication-failed VLANs do not receive reauthentication attempts if reauthentication is disabled. In order to start the reauthentication process the authentication-failed VLAN must receive a link down event or an EAP logoff event from the port. If the host is behind a hub, you may never get a link down event and may not detect the new host until the next reauthentication occurs. Therefore, it is recommended to have re-authentication enabled in that case.

•EAP failure messages are not sent to the user. If the user failures authentication the port is moved to an authentication-failed VLAN and a EAP success message is sent to the user. Because the user is not notified of the authentication failure there may be confusion as to why there is restricted access to the network. A EAP Success message is sent for the following reasons:

–If the EAP Success message is not sent, the user tries to authenticate every 60 seconds (by default) by sending an EAP-start message.

–In some cases, users have configured DHCP to EAP-Success and unless the user sees a success, DHCP will not work on the port.

•Sometimes a user caches an incorrect username and password combination after receiving a EAP success message from the authenticator and reuses that information in every re-authentication. Until the user passes the correct username and password combination the port remains in the authentication failed VLAN.

•When an authentication failed port is moved to an unauthorized state the authentication process is restarted. If you should fail the authentication process again the authenticator waits in the held state. After you have correctly reauthenticated all 802.1x ports are reinitialized and treated as normal 802.1x ports.

•When you reconfigure an authentication-failed VLAN to a different VLAN, any authentication failed ports are also moved and the ports stay in their current authorized state.

•When you shut down or remove an authentication-failed VLAN from the VLAN database, any authentication failed ports are immediately moved to an unauthorized state and the authentication process is restarted. The authenticator does not wait in a held state because the authentication-failed VLAN configuration still exists. While the authentication-failed VLAN is inactive, all authentication attempts are counted, and as soon as the VLAN becomes active the port is placed in the authentication-failed VLAN.

•If you reconfigure the maximum number of authentication failures allowed by the VLAN, the change takes affect after the reauthentication timer expires.

•All internal VLANs which are used for Layer 3 ports cannot be configured as an authentication failed VLAN.

•You cannot configure a VLAN to be both an authentication-failed VLAN and a voice VLAN. If you do, a syslog message is generated.

•The authentication-failed VLAN is supported only in single-host mode (the default port mode).

•When a port is placed in an authentication-failed VLAN the user's MAC address is added to the mac-address-table. If a new MAC address appears on the port, it is treated as a security violation.

•When an authentication failed port is moved to an authentication-failed VLAN, the Catalyst 4500 series switch does not transmit a RADIUS-Account Start Message like it does for regular 802.1X authentication.

Using 802.1X with Port Security

You can enable port security on an 802.1X port in either single- or multiple-host mode. (To do so, you must configure port security with the switchport port-security interface configuration command. Refer to the "Configuring Port Security" chapter in this guide.) When you enable port security and 802.1X on a port, 802.1X authenticates the port, and port security manages the number of MAC addresses allowed on that port, including that of the client. Hence an 802.1X port with port security enabled can be used to limit the number or group of clients that can access the network.

These examples describe the interaction between 802.1X and port security on the switch:

•When a client is authenticated, and the port security table is not full, the client's MAC address is added to the port security list of secure hosts. The port then proceeds to come up normally.

When a client is authenticated and manually configured for port security, it is guaranteed an entry in the secure host table (unless port security static aging has been enabled).

A security violation occurs if an additional host is learned on the port. The action taken depends on which feature (802.1X or port security) detects the security violation:

–If 802.1X detects the violation, the action is to err-disable the port.

–If port security detects the violation, the action is to shutdown or restrict the port (the action is configurable).

The following describes when port security and 802.1X security violations occur:

–In single host mode, after the port is authorized, any MAC address received other than the client's will cause a 802.1X security violation.

–In single host mode, if installation of an 802.1X client's MAC address fails because port security has already reached its limit (due to a configured secure MAC addresses), a port security violation is triggered.

–In multi host mode, once the port is authorized, any additional MAC addresses that cannot be installed because the port security has reached its limit will trigger a port security violation.

•When an 802.1X client logs off, the port transitions back to an unauthenticated state, and all dynamic entries in the secure host table are cleared, including the entry for the client. Normal authentication then ensues.

•If you administratively shut down the port, the port becomes unauthenticated, and all dynamic entries are removed from the secure host table.

•Only 802.1X can remove the client's MAC address from the port security table. Note that in multi host mode, with the exception of the client's MAC address, all MAC addresses that are learned by port security can be deleted using port security CLIs.

•Whenever port security ages out a 802.1X client's MAC address, 802.1X attempts to reauthenticate the client. Only if the reauthentication succeeds will the client's MAC address be retained in the port security table.

•All of the 802.1X client's MAC addresses are tagged with (dot1x) when you display the port security table by using CLI.

Using 802.1X with RADIUS-Provided Session Timeouts

802.1X enables the user to specify whether the switch uses a locally configured reauthentication timeout or a RADIUS-provided reauthentication timeout. If the switch is configured to use the local reauthentication timeout, it reauthenticates the host when the timer expires.

If the switch is configured to use the RADIUS-provided timeout, it looks in the RADIUS Access-Accept message for the Session-Timeout and optional Termination-Action attributes. The value of the Session-Timeout attribute is used to determine the duration of the session, and the value of the Termination-Action attribute is used to determine the switch action when the session's timer expires.

If the Termination-Action attribute is present and its value is RADIUS-Request, the switch reauthenticates the host. If the Termination-Action attribute is not present, or its value is Default, the switch terminates the session.

Note The supplicant on the port detects that its session has been terminated and attempts to initiate a new session. Unless the authentication server treats this new session differently, the client may see only a brief interruption in network connectivity as the switch sets up a new session.

If the switch is configured to use the RADIUS-supplied timeout, but the Access-Accept message does not include a Session-Timeout attribute, the switch never reauthenticates the supplicant. This behavior is consistent with Cisco's wireless access points.

Using 802.1X with RADIUS Accounting

802.1X RADIUS accounting relays important events to the RADIUS server (such as the client's connection session). This session is defined as the difference in time from when client is authorized to use the port and when the client stops using the port.

Enabling AAA system accounting along with 802.1X accounting allows system reload events to be sent to the accounting RADIUS server for logging. By doing this, the accounting RADIUS server can infer that all active 802.1X sessions are appropriately closed.

Because RADIUS uses the unreliable transport protocol UDP, accounting messages may be lost due to poor network conditions. If the switch does not receive the accounting response message from the RADIUS server after a configurable number of retransmissions of an accounting request, the following system message appears:

Use the show radius statistics command to display the number of RADIUS messages that do not receive the accounting response message.

Using 802.1X with Voice VLAN Ports

A voice VLAN port is a special access port associated with two VLAN identifiers:

•Voice VLAN ID (VVID) to carry voice traffic to and from the IP phone. The VVID is used to configure the IP phone connected to the port.

•Port VLAN ID (PVID) to carry the data traffic to and from the workstation connected to the switch through the IP phone. The PVID is the native VLAN of the port.

Each port that you configure for a voice VLAN is associated with a VVID and a PVID. This configuration allows voice traffic and data traffic to be separated onto different VLANs.

When you enable the single-host mode, only one 802.1X client is allowed on the primary VLAN; other workstations are blocked. When you enable the multiple-hosts mode and an 802.1X client is authenticated on the primary VLAN, additional clients on the voice VLAN are unrestricted after 802.1X authentication succeeds on the primary VLAN.

A voice VLAN port becomes active when there is a link whether or not the port is AUTHORIZED or UNAUTHORIZED. All traffic coming through the voice VLAN is learned correctly and appears in the MAC-address-table. Cisco IP phones do not relay CDP messages from other devices. As a result, if several Cisco IP phones are connected in series, the switch recognizes only the one directly connected to it. When 802.1X is enabled on a voice VLAN port, the switch drops packets from unrecognized Cisco IP phones more than one hop away.

When 802.1X is enabled on a port, you cannot configure a PVID that is equal to a VVID. For more information about voice VLANs, see "Configuring Voice Interfaces."

Be aware of the following feature interactions:

•802.1X VLAN assignment cannot assign to the port the same VLAN as the voice VLAN; otherwise, the 802.1X authentication will fail.

•802.1X guest VLAN works with the 802.1X voice VLAN port feature. However, the guest VLAN cannot be the same as the voice VLAN.

•802.1X port security works with the 802.1X voice VLAN port feature and is configured per port. Three secure addresses must be configured: one for the Cisco IP phone MAC address on the VVID, one for the PC MAC-address on PVID, and a third to allow the Cisco IP phone MAC address on the PVID.

•When 802.1X is configured on a port, you cannot connect multiple IP-phones to a Catalyst 4500 series switch through a hub.

•Because voice VLANs cannot be configured as private VLAN host ports, and because only private VLANs can be assigned to private VLAN host ports, VLAN assignment cannot assign a private VLAN to a port with a voice VLAN configured.

Supported Topologies

The 802.1X port-based authentication supports two topologies:

•Point to point

•Wireless LAN

In a point-to-point configuration (see Figure 29-1), only one client can be connected to the 802.1X-enabled switch port when the multi-host mode is not enabled (the default). The switch detects the client when the port link state changes to the up state. If a client leaves or is replaced with another client, the switch changes the port link state to down, and the port returns to the unauthorized state.

Figure 29-4 illustrates 802.1X port-based authentication in a wireless LAN. You must configure the 802.1X port as a multiple-host port that is authorized as a wireless access point once the client is authenticated. (See the "Enabling Multiple Hosts" section.) When the port is authorized, all other hosts that are indirectly attached to the port are granted access to the network. If the port becomes unauthorized (reauthentication fails or an EAPOL-logoff message is received), the switch denies access to the network for all wireless access point-attached clients. In this topology, the wireless access point is responsible for authenticating clients attached to it, and the wireless access point acts as a client to the switch.

The port transmits and receives normal traffic without 802.1X-based authentication of the client.

Periodic reauthentication

Disabled

Time between reauthentication attempts

3600 sec

Quiet period

60 sec

Number of seconds that the switch remains in the quiet state following a failed authentication exchange with the client.

Retransmission time

30 sec

Number of seconds that the switch should wait for a response to an EAP request/identity frame from the client before retransmitting the request.

Maximum retransmission number

2

Number of times that the switch will send an EAP-request/identity frame before restarting the authentication process.

Multiple host support

Disabled

Client timeout period

30 sec

When relaying a request from the authentication server to the client, the amount of time that the switch waits for a response before retransmitting the request to the client.

Authentication server timeout period

30 sec

When relaying a response from the client to the authentication server, the amount of time that the switch waits for a reply before retransmitting the response to the server. This setting is not configurable.

802.1X Configuration Guidelines

This section describes the guidelines for configuring 802.1X authentication:

•The 802.1X protocol is supported on both Layer 2 static-access ports and Layer 3 routed ports, but it is not supported on the following port types:

–Trunk port—If you try to enable 802.1X on a trunk port, an error message appears, and 802.1X is not enabled. If you try to change the mode of an 802.1X-enabled port to trunk, the port mode is not changed.

–Default ports—All ports default as dynamic-access ports (auto). Use the no switchport command to access a router port.

–Dynamic ports—A port in dynamic mode can negotiate with its neighbor to become a trunk port. If you try to enable 802.1X on a dynamic port, an error message appears, and 802.1X is not enabled. If you try to change the mode of an 802.1X-enabled port to dynamic, the port mode is not changed.

–EtherChannel port—Before enabling 802.1X on the port, you must first remove it from the EtherChannel. If you try to enable 802.1X on an EtherChannel or on an active port in an EtherChannel, an error message appears, and 802.1X is not enabled. If you enable 802.1X on a not-yet active port of an EtherChannel, the port does not join the EtherChannel.

–Switched Port Analyzer (SPAN) destination port—You can enable 802.1X on a port that is a SPAN destination port; however, 802.1X is disabled until the port is removed as a SPAN destination. You can enable 802.1X on a SPAN source port.

Enabling 802.1X Authentication

To enable 802.1X port-based authentication, you first must enable 802.1X globally on your switch, then enable AAA and specify the authentication method list. A method list describes the sequence and authentication methods that must be queried to authenticate a user.

The software uses the first method listed in the method list to authenticate users; if that method fails to respond, the software selects the next authentication method in the list. This process continues until there is successful communication with a listed authentication method or until all defined methods are exhausted. If authentication fails at any point in this cycle, the authentication process stops, and no other authentication methods are attempted.

To allow VLAN assignment, you must enable AAA authorization to configure the switch for all network-related service requests.

To create a default list that is used when a named list is not specified in the authentication command, use the default keyword followed by the methods that are to be used in default situations. The default method list is automatically applied to all interfaces.

Enter at least one of these keywords:

•group radius—Use the list of all RADIUS servers for authentication.

•none—Use no authentication. The client is automatically authenticated by the switch without using the information supplied by the client.

Step 5

Switch(config)# aaa authorization
network {default} group radius

(Optional) Configure the switch for user RADIUS authorization for all network-related service requests, such as VLAN assignment.

Step 6

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for 802.1X authentication.

To disable 802.1X authentication, use the dot1x port-control force-authorized or the no dot1x port-control interface configuration command.

This example shows how to enable AAA and 802.1X on Fast Ethernet port 2/1:

Switch# configure terminal

Switch(config)# dot1x system-auth-control

Switch(config)# aaa new-model

Switch(config)# aaa authentication dot1x default group radius

Switch(config)# interface fastethernet2/1

Switch(config-if)# dot1x port-control auto

Switch(config-if)# end

Configuring Switch-to-RADIUS-Server Communication

A RADIUS security server is identified by its host name or IP address, host name and specific UDP port number, or IP address and specific UDP port numbers. The combination of the IP address and UDP port number creates a unique identifier, which enables RADIUS requests to be sent to multiple UDP ports on a server at the same IP address. If two different host entries on the same RADIUS server are configured for the same service—for example, authentication—the second host entry configured acts as the fail-over backup to the first one. The RADIUS host entries are tried in the order they were configured.

To configure the RADIUS server parameters on the switch, perform this task:

For hostname | ip-address, specify the hostname or IP address of the remote RADIUS server.

For auth-port port-number, specify the UDP destination port for authentication requests. The default is 1812.

For acct-port port-number, specify the UDP destination port for accounting requests. The default is 1813.

For keystring, specify the authentication and encryption key used between the switch and the RADIUS daemon running on the RADIUS server. The key is a text string that must match the encryption key used on the RADIUS server.

Note Always configure the key as the last item in the radius-server host command syntax because leading spaces are ignored, but spaces within and at the end of the key are used. If you use spaces in the key, do not enclose the key in quotation marks unless the quotation marks are part of the key. This key must match the encryption used on the RADIUS daemon.

If you want to use multiple RADIUS servers, reenter this command.

Step 3

Switch(config-if)# ip radius
source-interface m/p

Establishes the IP address to be used as the source address for all outgoing RADIUS packets.

You can globally configure the timeout, retransmission, and encryption key values for all RADIUS servers by using the radius-server host global configuration command. If you want to configure these options on a per-server basis, use the radius-server timeout, radius-server retransmit, and the radius-server key global configuration commands.

You also need to configure some settings on the RADIUS server. These settings include the IP address of the switch and the key string to be shared by both the server and the switch.

Refer to the following Cisco IOS security documentation for information on how to configure AAA system accounting:

Configuring RADIUS-Provided Session Timeouts

You can configure the Catalyst 4500 series switch to use a RADIUS-provided reauthentication timeout.

To configure RADIUS-provided timeouts, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode.

Step 3

Switch(config-if)# dot1x-timeout
reauth-period {interface | server}

Sets the re-authentication period (seconds).

Step 4

Switch(config-if)# end

Returns to privileged EXEC mode.

Step 5

Switch # show dot1x interface

Verifies your entries.

Step 6

Switch # copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

This example shows how to configure the switch to derive the re-authentication period from the server:

Switch# configure terminal

Switch(config)# interface fa3/1

Switch(config-if)# dot1x timeout reauth-period server

Switch(config-if)# end

Switch)# show dot1x interface fa2/1

Enabling 802.1X Accounting

Note If you plan to implement system-wide accounting, you should also configure 802.1X accounting. Moreover, you need to inform the accounting server of the system reload event when the system is reloaded. Doing this, ensures that the accounting server knows that all outstanding 802.1X sessions on this system are closed.

After you configure 802.1X authentication and switch-to-RADIUS server communication, perform this task to enable 802.1X accounting:

Note You must configure the RADIUS server to perform accounting tasks, such as logging start, stop, and interim-update messages and time stamps. To turn on these functions, enable logging of "Update/Watchdog packets from this AAA client" in your RADIUS server Network Configuration tab. Next, enable "CVS RADIUS Accounting" in your RADIUS server System Configuration tab.

Configuring 802.1X with Guest VLANs

You can configure a guest VLAN for each 802.1X port on the Catalyst 4500 series switch to provide limited services to clients, such as downloading the 802.1X client. These clients might be upgrading their system for 802.1X authentication, and some hosts, such as Windows 98 systems, might not be 802.1X-capable.

When you enable a guest VLAN on an 802.1X port, the Catalyst 4500 series switch assigns clients to a guest VLAN provided (1) the authentication server does not receive a response to its EAPOL request or identity frame, or (2) the EAPOL packets are not sent by the client.

Prior to Cisco Release 12.2(25)EWA, the Catalyst 4500 series switch did not maintain the EAPOL packet history and allowed clients that failed authentication access to the guest VLAN, regardless whether EAPOL packets had been detected on the interface. You can enable this optional behavior with the dot1x guest-vlan supplicant global configuration command.

Starting with Cisco Release 12.2(25)EWA, the Catalyst 4500 series switch maintains the EAPOL packet history. If another EAPOL packet is detected on the interface during the lifetime of the link, network access is denied. The EAPOL history is reset upon loss of the link.

Any number of 802.1X-incapable clients are allowed access when the switch port is moved to the guest VLAN. If an 802.1X-capable client joins the same port on which the guest VLAN is configured, the port is put into the unauthorized state in the user-configured access VLAN, and authentication is restarted.

Guest VLANs are supported on 802.1X ports in single-host or multiple-hosts mode.

Note When a port is put into a guest VLAN, it is automatically placed into multihost mode, and an unlimited number of hosts can connect through the port. Changing the multihost configuration does not effect a port in a guest VLAN.

Except for an RSPAN VLAN or a voice VLAN, you can configure any active VLAN as an 802.1X guest VLAN. The guest VLAN feature is not supported on trunk ports; it is supported only on access ports.

To configure 802.1X with guest VLAN, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for 802.1X authentication.

To disable the guest VLAN feature on a particular port, use the no dot1x guest-vlan interface configuration command.

This example shows how to enable a regular VLAN 50 on Fast Ethernet 4/3 as a guest VLAN on a static access port:

Switch# configure terminal

Switch(config)# interface fa4/3

Switch(config-if)# switchport mode access

Switch(config-if)# dot1x port-control auto

Switch(config-if)# dot1x guest-vlan 50

Switch(config-if)# end

Switch#

This example shows how to enable a secondary private VLAN 100 as a guest VLAN on a private VLAN host port:

Switch# configure terminal

Switch(config)# interface fa4/3

Switch(config-if)# switchport mode private-vlan host

Switch(config-if)# dot1x port-control auto

Switch(config-if)# dot1x guest-vlan 100

Switch(config-if)# end

Switch#

To enable the optional guest VLAN behavior and to configure a guest VLAN, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch# dot1x guest-vlan supplicant

Enables the optional guest VLAN behavior globally on the switch.

Step 3

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for 802.1X authentication.

Step 4

Switch(config-if)# dot1x guest-vlan
vlan-id

Specifies an active VLAN as an 802.1X guest VLAN. The range is 1 to 4094.

Step 5

Switch(config)# end

Returns to privileged EXEC mode.

Step 6

Switch(config)# show dot1x
interface interface-id

Verifies your entries.

Step 7

Switch(config)# copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

To disable the optional guest VLAN feature on a particular port, use the no dot1x guest-vlansupplicant global configuration command.

This example shows how enable the optional guest VLAN behavior and to specify VLAN 5 as an 802.1X guest VLAN:

Switch# configure terminal

Switch(config)# dot1x guest-vlan supplicant

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# dot1x guest-vlan 5

Switch(config-if)# end

Switch#

Configuring 802.1X with Authentication Failed VLAN Assignment

You can configure Authentication Failed VLAN assignment on any Layer 2 port on the Catalyst 4500 series switch to provide limited network services to clients who fail the authentication process. You can use Authentication Failed VLAN assignment with other security features, such as Dynamic ARP Inspection (DAI), Dynamic Host Configuration Protocol (DHCP) snooping, and IP source guard. Each of these features can be enabled and disabled independently on the authentication-failed VLAN.

The port of a client who fails authentication is tagged as an "authentication failed" port and is placed in the authentication-failed VLAN. The port remains in the authentication failed VLAN until the reauthentication timer expires.

You can configure the maximum number of authentication attempts that the authenticator sends before moving a port into the authentication failed VLAN. The default value is 3. However, you may set the number as low as 1 and as high as 10. The authenticator keeps a count of the failed authentication attempts for each port. The number of failed authentication attempts is counted from the time of linkup to the point where the port is moved into the authentication failed VLAN. When the port is moved the counter is reset.

Note You cannot configure an authentication-failed VLAN and a voice VLAN on the same port. When you try to configure these two features on the same port, a syslog message is generated.

To configure 802.1X with authentication-failed VLAN assignment, follow these steps:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for 802.1X authentication.

Configure a maximum number of attempts before the port is moved to authentication-failed VLAN.

Default is 3 attempts.

Step 7

Switch(config-if)# end

Returns to configuration mode.

Step 8

Switch(config)# end

Returns to privileged EXEC mode.

To disable the authentication-failed VLAN feature on a particular port, use the no dot1x auth-fail vlan interface configuration command.

This example shows how to enable a regular VLAN 40 on Fast Ethernet 4/3 as a authentication failure VLAN on a static access port:

Switch# configure terminal

Switch(config)# interface gigabitethernet3/1

Switch(config-if)# switchport mode access

Switch(config-if)# dot1x port-control auto

Switch(config-if)# dot1x auth-fail vlan 40

Switch(config-if)# dot1x auth-fail max-attempts 5

Switch(config-if)# end

Switch(config)# end

Switch# show dot1x all

Dot1x Info for interface GigabitEthernet3/1

----------------------------------------------------

PortStatus = AUTHORIZED(AUTH-FAIL-VLAN)

MaxReq = 2

MaxAuthReq = 2

HostMode = Single(AUTH-FAIL-VLAN)

PortControl = Auto

QuietPeriod = 60 Seconds

Re-authentication = Disabled

ReAuthPeriod = 3600 Seconds

ServerTimeout = 30 Seconds

SuppTimeout = 30 Seconds

TxPeriod = 30 Seconds

Guest-Vlan = 6

Switch

Configuring 802.1X with Voice VLAN

To enable 802.1X with voice VLAN feature, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode.

Step 3

Switch(config-if)# switchport
access vlan vlan-id

Sets the VLAN for a switched interface in access mode.

Step 4

Switch(config-if)# switchport mode
access

Specifies a nontrunking, nontagged single VLAN Layer 2 interface.

Step 5

Switch(config-if)# switchport voice
vlan vlan-id

Sets the voice VLAN for the interface.

Step 6

Switch(config-if)# dot1x
port-control auto

Enables 802.1X authentication on the interface.

Step 7

Switch(config-if)# end

Returns to configuration mode.

Step 8

Switch(config)# end

Returns to privileged EXEC mode.

This example shows how to enable 802.1X with voice VLAN feature on Fast Ethernet interface 5/9:

Switch# configure terminal

Switch(config)# interface fastethernet5/9

Switch(config-if)# switchport access vlan 2

Switch(config-if)# switchport mode access

Switch(config-if)# switchport voice vlan 10

Switch(config-if)# dot1x port-control auto

Switch(config-if)# end

Note You must configure 802.1X and voice VLAN at the same time.

Enabling Periodic Reauthentication

You can enable periodic 802.1X client reauthentication and specify how often it occurs. If you do not specify a time value before enabling reauthentication, the interval between reauthentication attempts is 3600 seconds.

To enable periodic reauthentication of the client and to configure the number of seconds between reauthentication attempts, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for periodic reauthentication.

Step 3

Switch(config-if)# dot1x
re-authentication

Enables periodic reauthentication of the client, which is disabled by default.

Step 4

Switch(config)# dot1x timeout
reauth-period {seconds |server}

Specifies the number of seconds between reauthentication attempts or have the switch use a RADIUS-provided session timeout.

The range is 1 to 65,535; the default is 3600 seconds.

This command affects the behavior of the switch only if periodic reauthentication is enabled.

Step 5

Switch(config)# end

Returns to privileged EXEC mode.

Step 6

Switch# show dot1x all

Verifies your entries.

Step 7

Switch(config)# copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

To disable periodic reauthentication, use the nodot1x re-authentication interface configuration command. To return to the default number of seconds between reauthentication attempts, use the nodot1x timeout reauth-period global configuration command.

This example shows how to enable periodic reauthentication and set the number of seconds between reauthentication attempts to 4000:

Switch(config)# dot1x timeout reauth-period 4000

Switch(config)# dot1x re-authentication

Manually Reauthenticating a Client Connected to a Port

You can manually reauthenticate a client connected to a specific port at any time by entering the dot1x re-authenticate interfaceinterface-id privileged EXEC command. If you want to enable or disable periodic reauthentication, see the "Enabling Periodic Reauthentication" section.

This example shows how to manually reauthenticate the client connected to Fast Ethernet port 1/1:

Switch# dot1x re-authenticate interface fastethernet1/1

Starting reauthentication on FastEthernet1/1

Changing the Quiet Period

When the switch cannot authenticate the client, the switch remains idle for a set period of time, and then tries again. The idle time is determined by the quiet-period value. A failed authentication of the client might occur because the client provided an invalid password. You can provide a faster response time to the user by entering a number smaller than the default.

To change the quiet period, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for timeout quiet-period.

Step 3

Switch(config)# dot1x timeout
quiet-periodseconds

Sets the number of seconds that the switch remains in the quiet-period following a failed authentication exchange with the client.

The range is 0 to 65,535 seconds; the default is 60.

Step 4

Switch(config)# end

Returns to privileged EXEC mode.

Step 5

Switch# show dot1x all

Verifies your entries.

Step 6

Switch# copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

To return to the default quiet-period, use the no dot1x timeout quiet-period configuration command. This example shows how to set the quiet-period on the switch to 30 seconds:

Switch(config)# dot1x timeout quiet-period 30

Changing the Switch-to-Client Retransmission Time

The client responds to the EAP-request/identity frame from the switch with an EAP-response/identity frame. If the switch does not receive this response, it waits a set period of time (known as the retransmission time) and then retransmits the frame.

Note You should change the default value of this command only to adjust for unusual circumstances, such as unreliable links or specific behavioral problems with certain clients and authentication servers.

To change the amount of time that the switch waits for client notification, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for timeout tx-period.

Step 3

Switch(config-if)# dot1x timeout
tx-periodseconds

Sets the number of seconds that the switch waits for a response to an EAP-request/identity frame from the client before retransmitting the request.

The range is 1 to 65,535 seconds; the default is 30.

Step 4

Switch(config)# end

Returns to privileged EXEC mode.

Step 5

Switch# show dot1x all

Verifies your entries.

Step 6

Switch# copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

To return to the default retransmission time, use the no dot1x timeout tx-period interface configuration command.

This example shows how to set the retransmission time to 60 seconds:

Switch(config)# dot1x timeout tx-period 60

Setting the Switch-to-Client Frame-Retransmission Number

In addition to changing the switch-to-client retransmission times, you can change the number of times that the switch sends EAP-Request/Identity and other EAP-Request frames to the client before restarting the authentication process. The number of EAP-Request/Identity retransmissions is controlled by the dot1x max-reauth-req command; the number of retransmissions for other EAP-Request frames is controlled by the dot1x max-req command.

Note You should change the default values of these commands only to adjust for unusual circumstances such as unreliable links or specific behavioral problems with certain clients and authentication servers.

To set the switch-to-client frame-retransmission numbers, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interfaceinterface-id

Enters interface configuration mode and specifies the interface to be enabled for max-reauth-req and/or max-req.

Step 3

Switch(config-if)# dot1x max-reqcount

or

Switch(config-if)# dot1x max-reqcount

Specifies the number of times that the switch retransmits an EAP-request frame of a type other than EAP-request/identity to the client before restarting the authentication process.

Specifies the number of times that the switch retransmits an EAP-request/identity frame to the client before restarting the authentication process.

The range for count is 1 to 10; the default is 2.

Step 4

Switch(config)# end

Returns to privileged EXEC mode.

Step 5

Switch# show dot1x all

Verifies your entries.

Step 6

Switch# copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

To return to the default retransmission number, use the no dot1x max-req and no dot1x max-reauth-req global configuration command.

This example shows how to set 5 as the number of times that the switch retransmits an EAP-request/identity request before restarting the authentication process:

Switch(config)# dot1x max-reauth-req 5

Enabling Multiple Hosts

You can attach multiple hosts to a single 802.1X-enabled port as shown in Figure 29-4. In this mode, only one of the attached hosts must be successfully authorized for all hosts to be granted network access. If the port becomes unauthorized (reauthentication fails or an EAPOL-logoff message is received), all attached clients are denied access to the network.

To allow multiple hosts (clients) on an 802.1X-authorized port that has the dot1x port-control interface configuration command set to auto, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# interface
interface-id

Enters interface configuration mode and specifies the interface to which multiple hosts are indirectly attached.

Step 3

Switch(config-if)# dot1x host-mode
multi-host

Allows multiple hosts (clients) on an 802.1X-authorized port.

Make sure that the dot1x port-control interface configuration command set is set to auto for the specified interface.

Step 4

Switch(config-if)# end

Returns to privileged EXEC mode.

Step 5

Switch# show dot1x all interface
interface-id

Verifies your entries.

Step 6

Switch# copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

To disable multiple hosts on the port, use the no dot1x multiple-hosts interface configuration command.

This example shows how to enable 802.1X on Fast Ethernet interface 0/1 and to allow multiple hosts:

Switch(config)# interface fastethernet0/1

Switch(config-if)# dot1x port-control auto

Switch(config-if)# dot1x multiple-hosts

Resetting the 802.1X Configuration to the Default Values

To reset the 802.1X configuration to the default values, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# dot1x default

Resets the configurable 802.1X parameters to the default values.

Step 3

Switch(config)# end

Returns to privileged EXEC mode.

Step 4

Switch# show dot1x all

Verifies your entries.

Step 5

Switch# copy running-config
startup-config

(Optional) Saves your entries in the configuration file.

Displaying 802.1X Statistics and Status

To display 802.1X statistics for all interfaces, use the show dot1x statistics privileged EXEC command. To display 802.1X statistics for a specific interface, use the show dot1x statisticsinterfaceinterface-id privileged EXEC command.

To display the 802.1X administrative and operational status for the switch, use the show dot1x all privileged EXEC command. To display the 802.1X administrative and operational status for a specific interface, use the show dot1x interfaceinterface-idprivileged EXEC command.